A thread on NeoGAF
notes some code in the new Steam beta suggesting Valve is planning to allow
Steam users to select games to share with a circle of friends. This is confirmed
on
Kotaku, where they say Valve has not yet responded to the report (not a
shock since their story went up at 3:00 am on the west coast). Here is the code
in question:

"SteamUI_JoinDialog_SharedLicense_Title" "Shared game
library"
"SteamUI_JoinDialog_SharedLicenseLocked_OwnerText" "Just so you know, your games
are currently in use by %borrower%. Playing now will send %borrower% a notice
that it's time to quit."
"SteamUI_JoinDialog_SharedLicenseLocked_BorrowerText" "This shared game is
currently unavailable. Please try again later or buy this game for your own
library."

1) they are planning on releasing a steambox console, which would benefit from being able to trade/lend games to be a comparable alternative to the existing consoles.

2) all of the negative press surrounding XBone which has compared their strategy to steam. "well steam doesn't allow trading, and they're #1 on PC" if valve is half smart they will distance themselves from the xbone sinking ship

also they've supposedly been toying with this idea for years, it's not new, but the fallout from the xbone might be the push it needs to get rolling. the one silver lining of all that garbage.

A 'leet militia being necessary to the security of a free state, the right of the people to keep and bear virtual arms shall not be infringed! -Cutter